A number of thermoplastic compositions are very difficult to plasticize. In particular, thermoplastic compositions, including polypropylenes, are difficult to plasticize because it is difficult to find plasticizers that are sufficiently compatible with thermoplastic compositions. Consequently, exuding (bleeding) of plasticizer to the surfaces of an article comprising a thermoplastic composition frequently occurs upon cooling and crystallization of the thermoplastic composition.
Hydrocarbon-based processing oils such as naphthenic oils or paraffinic oils have been used to plasticize thermoplastics such as polypropylenes. While hydrocarbon-based processing oils can be used to plasticize thermoplastics with partial success, the resulting plasticized compositions lack advantageous low temperature properties. Moreover, the processing oils have a tendency to exude (bleed) to the surfaces of thermoplastic articles. Attempts to use conventional linear dibasic acid esters, such as dioctyl adipate or di-2-ethylhexyl sebacate, or phthalate esters, such as di-2-ethylhexyl phthalate, have also been unsuccessful since such conventional ester plasticizers are either incompatible with thermoplastics, resulting in exudation of the plasticizer, or are too volatile for many thermoplastic uses.
U.S. Pat. No. 5,290,886 teaches using organic ester plasticizers to plasticize thermoplastic elastomers comprising a blend of a thermoplastic polyolefin and an elastomer to lower the glass transition temperature (Tg) of both the elastomer and the polyolefin phases and to improve impact strength at low temperatures. The '886 patent neither discloses nor suggests using the cyclic dimerate and/or cyclic trimerate esters disclosed herein, and found that “polymeric dibasic esters and aromatic esters were found to be significantly less effective” (column 3, lines 62-64)
Dimer acid esters have been proposed as plasticizers for high temperature resistant fluorocarbon polymers (see U.S. Pat. No. 4,078,114) and for plasticizing anhydride-functionalized polymers (see U.S. Pat. No. 5,169,716), but have not been suggested for plasticizing non-fluorocarbon polymers or non-anhydride-functionalized polymers. It is preferred that the thermoplastics plasticized with the dimerate and/or trimerate esters disclosed herein are not fluorocarbon polymers or anhydride-functionalized polymers.
Surprisingly and unexpectedly, particular dimerate and/or trimerate esters designed to have very low polarity act as efficient plasticizers for thermoplastics. The resulting plasticized compositions have excellent low temperature properties and exhibit little or no tendency of the plasticizer to exude or bleed to the surface of a thermoplastic composition. Using the low polarity dimerate and/or trimerate esters as a plasticizer provides an advantageous balance of flexibility, impact resistance, and strength to thermoplastic-containing compositions.